The present invention relates to the manufacture of building materials and, more particularly, it relates to a method of heat-and-moisture treatment of articles such as concrete articles and to an apparatus for accomplishing same.
This invention can be used in the industry of building materials, in civil, rural and industrial construction for manufacturing articles from heavy, cellular and light concrete, silicate, foamed concrete and gypsum, as well as other building materials which need to be heat-and-moisture treated after molding.
There are presently known various methods of heat-and-moisture treatment of concrete, reinforced concrete and other articles, including those involving zone and sectional temperature control; in particular, in a circular tunnel chamber when specific thermal conditions are maintained in each one of the sections (zones), with the articles being subjected at one of the steps to the effect of superheated steam and carbon dioxide gas and, at the next step, to the effect of steam, after which the articles are treated with air and then cooled.
However, expensive prior art methods and apparatus for accomplishing same provide for heat treatment without controlling the relative humidity of the medium at all steps of heat treatment. While so doing, at the initial steps, upon the effect of superheated steam and then of steam with carbon dioxide gas, the continuity of the structure is disturbed considerably which leads to reduced strength. In addition, the use of the latter is rather expensive due to high capital costs.
There is also known a method for hardening and drying articles of light concrete, wherein the hardening of steam-treated articles is accelerated by using part of the moisture extracted from the articles in the course of drying them with hot air.
The latter method can only be used for drying light concrete articles and is absolutely inapplicable in the case of other types of concrete such as heavy concrete in view of dehydration and deterioration of all principal physical-and-mechanical characteristics of the latter.
There are other known methods of heat-and-moisture treatment of concrete articles, in particular, in a tunnel chamber with the aid of electric heaters attached to the inner walls of the chamber and serving to accelerate, by means of infrared radiation, the heat transfer to concrete, mainly ensuring the drying of the articles. The latter prior art method suffers from considerable non-uniformity of heat-treatment conditions over the chamber zones and stages while the thermodynamic parameters of the medium (temperature, humidity, velocity) sometimes fail to satisfy the conditions of heat-and-moisture treatment. This leads to deterioration of physical and mechanical parameters of articles and results in that this method is mainly suitable for use in the manufacture of ligh concrete articles, which restricts considerably the sphere of its application.
Also known in the art are methods of steam-heat treatment, which involve the provision in the chamber zones of autonomous heating and recirculation systems involving the use of aerodynamic-effect power units with additional heaters, with a possibility of supplying steam to the working space.
This and similar prior art methods suffer from difficulties in the discharge of the steam-gas phase from concrete and in the control over the relative humidity of the medium and over mass transfer, also leading to degradation. This results in a lower quality of the articles due to discontinuation of the growth of the strength of the concrete, as well as to reduced resistance to cold, durability and other qualitative factors. The latter method is only suitable for use with articles featuring a low modulus of exposed surface.
In view of the afore-listed disadvantages inherent in most of the above-cited prior art methods, further intensification of the process of heat-and-moisture treatment of articles becomes difficult and, in the case of some articles, simply impossible.